Dual Quantum Cascade Laser Micropackage

ABSTRACT

The present invention is directed to an ultra-compact dual quantum cascade laser assembly that nearly doubles the strength of a traditional laser in a in a single hermetically sealed micropackage. The device may comprise two quantum cascade lasers that meet at a combiner to create a single laser with a higher strength than traditional lasers. The current invention provides a path to an ultra-compact coherent beam combing arrangement that uses both dichroic beam combining and polarization beam combining techniques.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a continuation application of U.S. patentapplication Ser. No. 16/259,764 filed Jan. 28, 2019 which claims thebenefit of United States Provisional Patent Application Ser. No.62/622,759, entitled “Dual Quantum Cascade Laser Micropackage,” filedJan. 26, 2018, which applications are incorporated in their entiretyhere by this reference.

TECHNICAL FIELD

This invention relates to an ultra-compact coherent beam combingarrangement that may use both dichroic beam combining and polarizationbeam combining for compact packaging.

BACKGROUND

Many applications require coherent combination of two or more lasersproducing a single collimated, coaxial beam. These range fromexperiments in nonlinear optics (e.g., difference-frequency mixing) tospectroscopy applications such as Coherent Anti-stokes RamanSpectroscopy (CARS). Other applications requiring high brightness canalso benefit from the optical power addition of combining beams. Beamarrays are an example of a solution to high brightness using multiplebeam sources. Beam arrays using multiple beams that are spatiallylocated close to each other, but are not coaxial, do not produce acoherently combined beam, which will have a very poor beam quality.

SUMMARY

The present invention is directed to an ultra-compact dual quantumcascade laser assembly that nearly doubles the performance of atraditional laser in a single hermetically sealed micropackage. Thedevice may comprise two quantum cascade lasers with beam outputs thatmeet at a combiner to create a single laser beam with a higher powerthan traditional lasers. The current invention provides a path to anultra-compact coherent beam combing arrangement that uses both dichroicbeam combining and polarization beam combining ideas, never heretoforedeveloped for compact packaging.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a conceptual top view of the device in an embodiment usinga dichroic mirror;

FIG. 2 shows a perspective view of the device in an embodiment using adichroic mirror;

FIG. 3 shows a conceptual top view of the device in an embodiment usinga polarizer;

FIG. 4 shows a perspective view of the device in an embodiment using apolarizer;

FIG. 5 shows a perspective view of an embodiment of the hermeticallysealed micropackage;

FIG. 6 shows the results of a polarization beam combining arrangement;

FIG. 7 shows a photograph of a combined single beam emerging from anexperimental verification;

FIG. 8 shows the results of an dichroic beam combining arrangement; and

FIG. 9 shows a spectral scan of the single combined beam.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of presently-preferred embodimentsof the invention and is not intended to represent the only forms inwhich the present invention may be constructed or utilized. Thedescription sets forth the functions and the sequence of steps forconstructing and operating the invention in connection with theillustrated embodiments. It is to be understood, however, that the sameor equivalent functions and sequences may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the invention.

The present invention is directed to an ultra-compact dual quantumcascade laser assembly 100 that nearly doubles the performance of atraditional laser in a single hermetically sealed micropackage 122. Insome embodiments the present invention may comprise two lasers 102, 104,a combiner 112, two collimating lenses 106, 108, a reflector 110, and anexit port 118.

In some embodiments, the lasers may be, for example, quantum cascadelasers that may be the same wavelengths. The combiner may be a dichroicmirror 112, a polarizer 113, or some other method of combining beamsinto a singular beam 128.

Spectral Beam Combining

The device 100 may comprise two quantum cascade lasers 102, 104 thatemit laser beams 124, 126 and meet at a combiner 112 to create a singlebeam 128 with a higher performance than the beams of the individuallasers alone. The current invention provides a path to an ultra-compactcoherent beam combing arrangement that uses both dichroic beam combiningor polarization beam combining ideas, never heretofore developed forcompact packaging. Spectral beam combining may be achieved using acombiner 112, which may be a dichroic mirror, polarizer, or othervarious elements.

FIGS. 1 and 2 demonstrate current devices showing two beams summing whenthe wavelengths of two beams 124, 126 differ from each other byapproximately 100 nm, dichroic mirror coatings can be developed or areoften available for reflecting one beam 124 while transmitting the otherbeam 126. In some embodiments of combining the beams, the present devicemay be configured to spatially and directionally match the beams 124,126 to yield a single collimated, coaxial output beam 128.

This may be accomplished by configuring the device so the two beams 124,126 meet at the same physical location on the reflecting surface of adichroic mirror 112 which may be accomplished by correctly pointing andaligning the collimated beams 124, 126 from separate quantum cascadelasers 102, 104.

In an embodiment of the invention the device may be configured toarrange the angular alignment of the two beams 124, 126 at the samephysical location on the dichroic mirror 112, through minor adjustmentof the path of the beam from a first laser 102, while keeping thephysical location of its beam 124 unchanged on the reflecting surface ofthe dichroic mirror 112.

In some embodiments a dual laser micropackage 100 is configured tocombine two lasers 102, 104, which may emit beams of differentwavelengths 124, 126. For example, in some embodiments, this structuremay include one laser 102 that emits a beam 124 at approximately 4.0micrometer and another laser 104 that emits a second beam 126 atapproximately 4.6 micrometer.

For example, FIG. 2 shows the internal construction of an embodiment ofthe dual laser micropackage 100 wherein the device is configured toutilize two lasers 102, 104, two collimating lenses 106, 108, areflector 110, and a dichroic mirror as the beam combiner 112. In thisembodiment there are two lasers 102, 104 configured to output beams 124,126 with a wavelength of approximately the 4.0 micrometer and 4.6micrometer respectively. The quantum cascade lasers may be mounted on,for example, a copper heat spreader 116. In this embodiment each lasermay have four electrical pins 114 at the rear of the device 100, two maybe for driving the lasers 102, 104 and two may be for laser temperaturemonitoring. The beams 124, 126 output from each of the lasers 102, 104may be collimated using high numerical aperture lenses 106, 108. Thereflector 110 and the dichroic beam combiner 112 may be aligned andpermanently affixed in position for long-term stability. This embodimentmay be configured to have, for example, 4.0 micrometer and 4.6micrometer beams 124, 126 emerge from the laser package as a single beam128. The single beam 128 may be, for example, a collimated coaxial beam128. Alignment of the beams 124, 126 may be achieved in this embodimentby adjustment of the collimating lenses 106, 108 on the individuallasers 102, 104, which may allow for small changes in X-Y position andpointing before the collimating lenses 102 and 106 are permanentlyaffixed in their respective positions and sealing the contents of thedevice in a hermetically sealed micropackage 100.

In some embodiments, the first quantum cascade laser and the secondquantum cascade laser may be positioned parallel to each other. Thefirst laser may be configured to emit a first laser beam defining afirst path. The second laser may be configured to emit a second laserbeam defining a second path.

Additionally, the first collimating lens may be positioned adjacent tothe first laser in line with the first path and the second collimatinglens may be positioned adjacent to the second quantum cascade laser inline with the second path. The reflector may be positioned adjacent tothe first collimating lens and at an approximately 45 degree anglerelative to the first path to cause the first laser beam to emit along athird path perpendicular to the first path. The dichroic mirror may bepositioned adjacent to the reflector and adjacent to the secondcollimating lens so as to form an approximately a 45 degree angle withthe second path and an approximately 45 degree angle with the thirdpath.

Polarization Beam Combining

In another embodiment of FIG. 4, to coherently combine radiation fromtwo lasers 102, 104 the device may be configured to emit broadbandradiation, which may be, for example, similar to that of Fabry Perotconfiguration quantum cascade lasers. In some embodiments, the lasers102, 104 may be configured to emit beams 124, 126 at the samewavelength. However, it should be noted that polarization beam combiningdoes not require the two laser wavelengths be nearly the same. By same,we do not mean exactly the same. Furthermore, the polarization beamcombining scheme will may work with any combination of laserwavelengths. But, if the two wavelengths are approximately the same,polarization beam combining may be required. When an embodiment isconfigured to have the lasers 102, 104 configured to emit beams 124, 126to be at the same wavelength, polarization beam combining techniquesbecome necessary, which may require linearly polarized output beams 124,126 from both lasers 102, 104. In an embodiment of the presentinvention, the lasers 102, 104 are configured to naturally emit linearlypolarized light output beams 124, 126 along a first and second pathrespectively. The two linearly polarized output beams 124, 126 may beorthogonal, and may be combined using a polarizer 112 that will reflectone polarized beam 124 while transmitting the other orthogonallypolarized beam 126. The polarizer 112 may be a wire grid polarizer orvarious other types of polarizers. The resulting beam 128 becomesunpolarized. The outputs from the lasers 102, 104 may be linearlypolarized, however, an embodiment of the present device may beconfigured to rotate the polarization of one of the quantum cascadelasers 102 by 90°, using a half wave plate 120.

FIG. 3 shows a schematic of the polarization beam combining technique.As was with the embodiment using a dichroic beam combining technique(FIGS. 1 and 2), the combined beam 128 may have both beams 124, 126spatially and directionally matched to yield a single collimated coaxialoutput beam 128.

In some embodiments, the two beams 124, 126 meet at the same physicallocation on the reflecting surface of a polarizer 112, which may beaccomplished by correctly pointing collimated output beams 124, 126 fromtwo different lasers 102, 104.

The angular alignment of the two beams 124, 126, which may be located onthe same physical location on a polarizer 112, may be achieved by minoradjustment of the pointing direction of the beam 124 from a first laser102, while keeping the physical location of its beam unchanged on thereflecting surface of the polarizer 112.

In some embodiments of the present device, the dual laser micropackagedesign 100 may be configured to combine two beams 124, 126 of the samewavelength output from lasers 102, 104. For example, an embodiment mayinclude, for example, two lasers 102, 104 that output beams 124, 126with a wavelength of 4.6 micro-meters.

FIG. 4 shows the internal configuration of an embodiment of a lasermicropackage 100 using the polarization techniques described above. Inthis embodiment, two lasers 102, 104, both outputting beams 124, 126 at,for example, 4.6 micrometers, may be mounted on a heat spreader 116. Theheat spreader 116 may be a copper heat spreader or other suitable highconductivity metallic heat spreaders. Each laser 102, 104 may have fourelectrical pin connections 114 at the rear of the package, two may befor driving the lasers 102, 104 and two may be for quantum cascade lasertemperature monitor thermistor. In some embodiments, the output beam124, 126 from each of the lasers 102, 104 may be linearly polarized(vertical) and may be collimated using high numerical aperture lenses106, 108. The first beam 124 may pass through a half wave plate 120 thatrotates the first beam's polarization by approximately 90 degrees. Thisprocess may result in the beam 124 being incident onto the polarizer112. The polarizer 112 may be configured to reflect a first laser's beampolarization 124, while transmitting an orthogonal polarization of thebeam 126 from a second laser 104. In some embodiments, the half waveplate 120, the reflector 110, and the polarizer 112 may be aligned andpermanently affixed in position for long-term stability. The componentsmay also be secured by means such as cements, glues, welding, or othersuitable means for attachment, resulting in a secure device 100 with nomoving parts. In some embodiments, for example, 4.6 micrometers beams124, 126 may emerge from the laser package as a collimated coaxial beam128. Final alignment of the beams 124, 126 may be achieved byadjustments of the collimating lenses 106, 108, which may allow forsmall changes in X-Y position and angular pointing before curing theglue or otherwise permanently securing the components of the device intothe micropackage 100.

In some embodiments the first quantum cascade laser and the secondquantum cascade laser may be positioned parallel to each other. Thefirst laser may be configured emit a first laser beam defining a firstpath. The second laser may be configured to emit a second laser beamdefining a second path. The first collimating lens may be positioneddirectly adjacent to the first quantum cascade laser in line with thefirst path and the second collimating lens may be positioned directlyadjacent to the second quantum cascade laser in line with the secondpath. The half-wave plate may positioned adjacent to the firstcollimating lens in line with the first path. The reflector may bepositioned adjacent to the half-wave plate and at an approximately 45degree angle relative to the first path to cause the first laser beam toemit along a third path perpendicular to the first path. The wire gridpolarizer may be positioned adjacent to the reflector and adjacent tothe second collimating lens so as to form an approximately a 45 degreeangle with the second path and a 45 degree angle with the third path.The exit port may be located adjacent to the wire grid polarizer.Finally, the first laser and the second laser combine into aconsolidated third laser at the wire grid polarizer and the consolidatedthird laser may pass through the exit port.

In some embodiments as shown in FIG. 5, the present invention may beconfigured to implement a miniature micropackage 100 to provide thecapability of installing two lasers 102, 104, that emit beams 124, 126of the same color (wavelength) or of differing colors (wavelengths) in asingle hermetically sealed micropackage 100 along with the necessaryoptical components shown in, for example, FIGS. 2 and 4. Permanentalignment of the optical beam combining elements may be achieved throughexacting tolerances in manufacturing. In some embodiments, the devicemay be configured so that the only components that are adjustable duringthe fabrication process are the beam collimating lenses 106, 108 for theindividual lasers 102, 104 that may permit small adjustments in beam124, 126 location and direction. In such an embodiment, once thecollimating lenses 106, 108 are correctly positioned, they may bepermanently affixed in their locations (as may be the other opticalcomponents) to provide a final micropackage 100 that meets MIL-STD 810Genvironmental standards.

In some embodiments, the micropackage may house two lasers 102, 104 asshown in, for example, FIGS. 2 and 4. In some embodiments, themechanical dimensions of the micropackage 100 may be approximately 1.25″(W)×1.40″ (D)×0.42″ (H). The complete assembly may weigh, for exampleless than 55 grams. In other embodiments, the dimensions may be adjustedfor different internal configurations with similar volume and weight.

To assure ruggedness, some embodiments of the dual laser micropackage100 may be configured to have no moving parts. All optics within anembodiment of the present micropackage may be glued using optical UVcuring cements. Additionally, in another embodiment the optics may besecured by other various adhesives such as cement, and glue or throughusing laser welding. The present invention may be configured to complywith MIL-STD 810G environmental requirements.

In an embodiment of the present invention the micropackage 122 may beconfigured to be hermetically sealed to provide an inert internalatmosphere.

In FIG. 4, the two quantum cascade lasers (“QCL”), QCL1 102 and QCL2104, may produce broad band laser outputs at approximately 4.6micro-meters with power levels of approximately 1.73 W and 1.39 W,respectively. Both laser outputs may be vertically polarized and may becollimated using the lenses 106, 108 shown. Collimated laser radiationfrom QCL1 102 may pass through the half-wave plate 120, which rotatesthe polarization of QCL1 102 radiation by 90 degrees, making thepolarization horizontal. The reflector 110 may turn the direction of theQCL1 102 radiation by a right angle and the radiation may becomeincident on the wire grid polarizer 112. The wire grid polarizer 112 maybe arranged so as to reflect the horizontally polarized light output,thus, the QCL1 102 radiation may now be coming down in FIG. 4. In someembodiments such as the collimated QCL2 104, radiation, which may bevertically polarized, passes through the wire grid polarizer 112unimpeded. The directions and positions of the radiations from the twoQCLs, at their meeting place on the wire grid polarizer 112, may beadjusted so that the two beams meet at the same location on thepolarizer 112 (at the reflecting surface for QCL2 104 radiation) andupon reflection of the QCL1 102 radiation and transmission of QCL2 104radiation, the two beams may emerge collinearly and coaxially.

FIG. 6 documents the results of some embodiments of beam combining. Thecombined single coaxial beam may have a power output of approximately3.06 W, corresponding to a loss of approximately less than 2 percentfrom the total of the individual laser outputs, confirming the highefficiency of beam combining.

FIG. 7 documents the beam combing feature of some embodiments of theinvention by providing a photograph of the 3.06 W beam emerging from thebeam combiner, taken at a distance of 1.8 m from the exit of the beamcombiner. A single beam image confirms the beam combining efficacy ofthe invention.

FIG. 2 shows a demonstration of beam combining for some embodiments ofthe invention where the two laser beams may have different wavelengths.QCL1 102 may be a laser at approximately 4.0 micro-meters producing apower of about 1.0 W and QCL2 104 may be a laser at approximately 4.6micro-meters, producing a power output of about 1.5 W. Power outputs ofboth QCLs 102, 104 may be vertically polarized and may be collimatedusing the collimating lenses 106, 108 as shown. In FIG. 2, both beamsmay be propagating horizontally and to the left. The collimated QCL1 102beam may be reflected from the reflector and may now be coming downvertically in the figure and it may be reflected from the front face ofthe dichroic mirror 112 as shown. The dichroic mirror 112 may be highlyreflecting at approximately 4.0 micro-meters and may be highlytransmissive at approximately 4.6 micro-meters. The reflected QCL1 102light may now emerging horizontally, as seen in the figure. Collimatedlight output from QCL2 104 travelling horizontally in the figure, maypass through the dichroic mirror 112 at the same spot where the QCL1 102radiation is reflected. The reflected QCL1 102 light may now emerginghorizontally, as seen in the figure. The combined beam may now containQCL1 102 radiation at approximately 4.0 micro-meters and the QCL2 104radiation at approximately 4.6 micro-meters, which may be collinear andcoaxial.

FIG. 8 shows the results the dichroic beam combing invention in someembodiments. The total power output may now be approximately 2.4 W,corresponding to approximately less than 4 percent loss of power of thetwo individual beams.

FIG. 9 shows some embodiments of spectral analysis of the singlecombined beam emerging from the arrangement in FIG. 9, the analysis maybe carried out using a Fourier Transform Infrared Spectrometer. Bothradiations, one at approximately 4.0 micro-meters and the other atapproximately 4.6 micro-meters are simultaneously available in a singlebeam.

In both cases, FIGS. 2 and 4, the platform on which the beam combiningwas accomplished may eventually be packaged inside a hermetically sealedpackage shown in FIG. 5.

The foregoing description of the preferred embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention not be limited by this detailed description, but by the claimsand the equivalents to the claims appended hereto.

What is claimed is:
 1. An ultra-compact dual quantum cascade laserassembly comprising: a. a first quantum cascade laser; b. a secondquantum cascade laser; c. a combiner; d. a first collimating lens; e. asecond collimating lens; f. a reflector; g. an exit port; and h. asingle hermetically sealed micropackage; i. wherein the first quantumcascade laser is positioned adjacent to the second quantum cascadelaser; j. wherein the reflector is positioned between the firstcollimating lens and the combiner; k. wherein the combiner is positionedbetween the reflector and the second collimating lens; l. wherein theexit port is located adjacent to the combiner; m. wherein the firstquantum cascade laser and the second quantum cascade laser areconfigured to produce a first laser beam and a second laser beam thatcombine into a consolidated third laser beam and the consolidated thirdlaser beam is configured to pass through the exit port.
 2. Theultra-compact dual quantum cascade laser assembly of claim 1, whereinthe first quantum cascade laser, the second quantum cascade laser, thecombiner, the first collimating lens, the second collimating lens, andthe reflector are all contained within the single hermetically sealedmicropackage.
 3. The ultra-compact dual quantum cascade laser assemblyof claim 2, wherein the first laser beam has a first wavelength and thesecond laser beam has a second wavelength, wherein the first and thesecond wavelengths are approximately equal.
 4. The ultra-compact dualquantum cascade laser assembly of claim 3, wherein a weight of theultra-compact dual quantum cascade laser is less than 70 grams.
 5. Theultra-compact dual quantum cascade laser assembly of claim 4, whereinthere are no moving parts in the ultra-compact dual quantum cascadelaser assembly.
 6. The ultra-compact dual quantum cascade laser assemblyof claim 5, wherein a combined power loss of the first laser beam andthe second laser beam when combined into the consolidated third laserbeam is less than 6 percent of a sum of a power of the first laser beamand a power of the second laser beam.
 7. The ultra-compact dual quantumcascade laser assembly of claim 6, wherein a volume of the hermeticallysealed micropackage is less than 6.25 cubic inches.
 8. An ultra-compactdual quantum cascade laser assembly comprising: a. a first quantumcascade laser; b. a second quantum cascade laser; c. a combiner; d. afirst collimating lens; e. a second collimating lens; f. a reflector; g.an exit port; and h. a hermetically sealed micropackage; i. wherein thefirst quantum cascade laser, the second quantum cascade laser, thecombiner, the first collimating lens, the second collimating lens, andthe reflector are all contained within the hermetically sealedmicropackage; j. wherein the first quantum cascade laser is positionedadjacent to the second quantum cascade laser; k. wherein the reflectoris positioned between the first collimating lens and the combiner; l.wherein the combiner is positioned between the reflector and the secondcollimating lens; and m. wherein the first quantum cascade laser and thesecond quantum cascade laser are configured to produce a first laserbeam and a second laser beam to combine into a consolidated third laserbeam and the consolidated third laser beam is configured to pass throughthe exit port.
 9. The ultra-compact dual quantum cascade laser assemblyof claim 8, wherein the exit port is within a wall of the hermeticallysealed micropackage, sealed with an anti-reflection coated window. 10.The ultra-compact dual quantum cascade laser assembly of claim 8,wherein the first laser beam has a first wavelength and the second laserbeam has a second wavelength, wherein the first and the secondwavelengths are approximately equal.
 11. The ultra-compact dual quantumcascade laser assembly of claim 8, wherein the weight of theultra-compact dual quantum cascade laser is less than 70 grams.
 12. Theultra-compact dual quantum cascade laser assembly of claim 8, whereinthere are no moving parts in the ultra-compact dual quantum cascadelaser assembly.
 13. The ultra-compact dual quantum cascade laserassembly of claim 8, wherein a combined power loss of the first laserbeam and the second laser beam when combined into the third laser beamis less than 6 percent of a sum of a power of the first laser beam and apower of the second laser beam.
 14. The ultra-compact dual quantumcascade laser assembly of claim 8, wherein a volume of the hermeticallysealed micropackage is less than 6.25 cubic inches.
 15. Theultra-compact dual quantum cascade laser assembly of claim 8, whereinthe combiner is a dichroic mirror.
 16. The ultra-compact dual quantumcascade laser assembly of claim 8, wherein the combiner is a polarizer.17. The ultra-compact dual quantum cascade laser assembly of claim 8,wherein a polarization of the second laser beam is made orthogonal tothe polarization of the first laser beam using a half wave plate. 18.The ultra-compact dual quantum cascade laser assembly of claim 8,wherein the first quantum cascade laser and the second quantum cascadelaser are mounted on a copper heat spreader.
 19. The ultra-compact dualquantum cascade laser assembly of claim 8, wherein the first quantumcascade laser and the second quantum cascade laser each have fourcorresponding electrical pins.
 20. The ultra-compact dual quantumcascade laser assembly of claim 8, wherein two of the four correspondingelectrical pins are configured to drive the lasers and the other two ofthe four corresponding electrical pins are configured for temperaturemonitoring.
 21. The ultra-compact dual quantum cascade laser assembly ofclaim 8, wherein the first collimating lens and the second collimatinglens are adjustable during assembly to permit small adjustments indirection.